It is sometimes necessary to evacuate moist air from equipment such as chambers or vessels. For example, a vacuum pump can be used to evacuate air from a chamber containing a moist or wet object. However, if moist air is pulled into a vacuum pump, it can negatively impact the efficiency of the pump and reduce the lifetime of the pump.
In the construction industry, vacuum pumps can be used in the testing of paving materials. By way of example, compacted asphalt samples are tested using ASTM Test D2726, ASTM Test D6752, and AASHTO Test T166. These tests require the determination of the density of the materials. This requires that the dry mass of a sample along with a sample volume be determined in order to calculate the density, which is the ratio of the mass to the volume. Moisture may be introduced into the sample by the cutting process or may be naturally present in the sample. As described in U.S. Patent Application Publication No. 2005/0102851, the disclosure of which is incorporated by reference herein in its entirety, a vacuum pump can be used to remove moisture from a chamber holding the sample to thereby dry the sample.
By way of further example, vacuum pumps can be used in tests to determine the maximum specific gravity and density of bituminous paving mixtures, such as the tests described in ASTM Test D2041 and AASHTO Test T209. In these tests, a sample of known dry weight is placed in a vessel. Water is then introduced into the vessel to submerge the sample, and the vacuum pump evacuates air to reduce the pressure in the vessel. The volume of the sample is then determined, and the density or specific gravity of the sample can be determined based on the dry weight and the volume of the sample.
As seen from these examples, the vacuum pump may evacuate moist air from the chamber or vessel. The evacuated moist air will enter the vacuum pump unless it is dried prior to reaching the pump. Vacuum pumps use lubricants (e.g., oil) to reduce friction between moving parts and to protect seals. However, when moisture enters the vacuum pump, the moisture mixes with the oil and reduces its effectiveness. Thus, moisture will eventually destroy the vacuum pump. Frequent oil changes may prolong the life of the pump, but the oil changes can frustrate the user by increasing cost and creating downtime, and can also produce considerable waste.
Therefore, users sometimes attempt to dry the air before it enters the pump. Indeed, the aforementioned ASTM Test D2041 and AASHTO Test T209 require the use of one or more in-line dryers to reduce moisture entering the vacuum pump. Current practice is to use one or more desiccant air dryers positioned between the equipment containing moist air and the vacuum pump.
However, there are numerous drawbacks to the use of presently used in-line dryers, such as desiccant dryers. First, desiccant dryers can introduce considerable air flow resistance, thereby increasing the power consumed by the vacuum pump and decreasing its efficiency.
Moreover, desiccant dryers can be inefficient with regard to their moisture-removing characteristics. The dryers tend to be most efficient when the desiccants are dry. Thus, the dryers will either lose their efficiency during use or will create downtime while waiting for the desiccants to dry. The dryers could be replaced or recycled during use, but this increases cost and also creates downtime.
Desiccant dryers have a limited lifetime, and need to be replaced or recycled periodically. Again, this increases cost and creates downtime. The continual replacement also produces waste. Furthermore, a user may neglect to timely replace the dryers, which can decrease the efficiency and reduce the life of the vacuum pump.
Thus, the current use of desiccant dryers can be environmentally unfriendly. The dryers increase air flow resistance and can allow moisture into the vacuum pump, which can increase the necessary power consumed by the pump. Moisture entering the pump also reduces the efficiency of the lubricant or oil in the pump, necessitating an increased number of waste-creating oil changes. Finally, because the desiccant dryers inevitably allow moisture to enter the vacuum pump, the life of the vacuum pump is decreased, sometimes substantially. The result can be the early disposal and replacement of pumps.
Therefore, there may be a need for an apparatus that will effectively dry air evacuated from equipment before the air enters the vacuum pump, and will do so without overly restricting air flow. There may be a need for an apparatus that will perform effective drying continuously to minimize downtime. Finally, there may be a need for an environmentally friendly solution that can increase the lifetime of vacuum pumps and generally reduce waste.